1. Field of this Invention
This invention relates to a process for the determination of the vasco-elastic characteristics of polymers and an arrangement for conducting the process.
2. Prior Art
The visco-elastic characteristics of polymers have been determined by means of a torsional oscillation apparatus. In that case a test strip of certain dimensions from the pertinent polymer is held first at one end and, at the other end, an oscillation body is attached; the pendulum formed thereby is stimulated as a result thereby in a heatable chamber to torsional oscillations, and the frequency and attenuation of the oscillations is measured. The known process is indeed simple in principle and it makes possible a precise determination of the physically defined elasticity and rigidity moduli and of the attenuation. But execution of such process is cumbersome and time consuming and correspondingly expensive.
For example, it is cumbersome to get the test strip, as required, exactly symmetrical with regard to the torsion pendulum axis in the apparatus and to insert it in its clumped state into its heatable chamber. The process is time consuming because the test strip lies unfettered in the chamber on its periphery, and thus can be heated or cooled only by radiation and convection.
The constant measuring frequency over the entire temperature range, which is to be strived for from the physical point of view, cannot be achieved, or can only be achieved only at additional cost, with known torsional oscillation apparatus.
The known process also has the basic disadvantage created by the principle of measurement in that mesurements can only be made in the range of temperatures at which the test strip can be used as a torsion of a torsion pendulum. Above a certain softening temperature, no measurements can be made according to this principle.
The reasons why the known torsional oscillation apparatuses are expensive and correspondingly costly are that various problems occur during execution of the known process.
The precise clamping down of the test strip in the correct position with respect to the vibrating body requires a special clamping apparatus. It is difficult to stimulate the pendulum to carry out a purely rotating oscillation, i.e., to avoid translatory oscillation components, which would lead to errors in measurement. The oscillation amplitudes of only a few angular degrees, which are small in the linear elasticity range for the purpose of measurement, can be measured only by means of Poggendox's reading by reflection or by means of a precisely operating electromechanical converter. While passing through the temperature range, the test strip is gradually twisted, whereby the zero point of the oscillation migrates by a certain amount which in comparison to the amplitude is not negligible under any circumstances.
The test strip therefore must be connected to the oscillating body by a connecting element, rotatable without friction with respect to the heatable chamber, whereby its guidance through the chamber wall must not lead to a significant heat exchange between the space within and the space without the chamber. In order to avoid a longitudinal tension which could distort the measuring results, said strip must be released of the weight of the oscillating body.
The structural solution of these problems led the art to expensive and corresponding costly torsional oscillation arrangements.
For these reasons, the visco-elastic characteristics of polymers could be determined hitherto only in larger research laboratories. There was no simple, little-time consuming process which could be carried out with a reasonably priced apparatus which was available to the practitioner for these purposes.